Recoilless firearm and ammunition therefor



Y @VE Mag June 7, 1949. w.'J. KROEGER Er A1.

RECOILLESS FIREARM AND AMMUNITION THEREFQR Filed Feb. 14. 1945 v June 71949- w. J. KROEGER E1' AL 2,472,111

RECOILLESS FIREARM AND MMUNITION THEREFOR Filed Feb'. 14, 1945 4Sheets-Sheet 2 Mussel?,

.lune 7, 1949. w. J. KROEGER Er A1.

RECOILLESS FIREARM AND AMMUNITION THEREFORA Fiie'd Feb. 14, 1945 4Sheets-Sheet 3 ILLIAMtLKRDEEER, W ALTCIN Museen,

fm" d. WMMMA June 7, 1949. Aw. J. KRoEGl-:R 1=:r A1.

RECOILLES S FIREARM AND AMMUNITION THEREFOR 4 sheis-sheet 4 Filed Feb.14, 1945 Patented June 7., 1949- f -llECOILLESS FIREARM AND AMMUNITIONTHEREFOR William J. Kroeger and Clarence Walton Musser,

i f Philadelphia, Pa.

Application February 14, 1945, Serial No. 577,830V

` claims. (ci. ssi- 1.7)

(Granted under the act cf March vamended April 30, 1928; 370 0.

The invention described herein may be manufactured and used by orforgtheGovernment for governmental purposes. without the payment to us of any,royalty thereon. y l .Ouzr invention relates'to firearms of therecoillesstype and it has special reference to non-recoil guns whereinthe forces of rearward reaction that result from projectile dischargeare neutralized I by forwardly acting counterforces simultaneously setup by a rearward escape of propellent powder gas through openings `ororices in the guns breach.

Bnoadly stated, the obiect of our invention is to improve the design andextend the usefulness of recoilless guns which incorporate principles ofconstruction and operation first disclosed and claimed by our co-pendingyapplication Serial No. 536,590, filed May 20, 1944, and now abandoned,for Recoilless irearms, ammunition therefor, and ballistic design thereov n A more specic object is to provide for such "openbreech" recoillessguns unique weapon designs and constructions which are` peculiarlyadapted to firearms 05,75 millimeter .and other high calibelS.

Another object isto provide improved cham"- ber and breech constructionsfor recoilless guns which utilize the annular orifice and the perforatedcartridge case principles of our earlier application above identified.

A further'obiect is kto facilitate adjustment of breech orifice area andthe vsecuring of zero recoil at a desired performance level.

- A still furtherobject is to increase the simplicity, ruggedness andcompactness of breech actions and of firingv and safety mechanisms forrecoilless firearm use. v

An additional object is to make possible the practical Vconstruction andsuccessful use of large caliber recoilless firearms which are capable ofshooting projectiles carrying heavy quantities of explosive through longdistances and yet which are so relatively light in weight and so compactin size as to be readily portable.

Other objects and advantages will become apparent as the disclosure anddescription hereof proceeds.

Y vbarrels end toward the 'chambers breech; we ad- 3, 1883, as G. 757)just breech orliice area through the medium of a replaceable cone ofunique design and mounting; and we provide improved breech extractor andfiring and safety mechanisms which are simpler. more compact and rugged.and which are coordinated in a unique way and more convenient loadingand firing.

O ur invention itself together with illustrative embodiments thereofwill best be understood from the following description when taken inconjunction with the accompanying drawings wherein:

Fig. 1 is a perspective view of a recoilless gun of '75 mm. caliberwhich incorporates our inven- 1 tive features and which is shown asbeing supported from a tripod for convenient aiming and firing;

Fig. 2 illustrates the recoilless guns internal construction insimplified schematic form;

Fig. 3 shows our weapon ln rear elevation with the breech bar and breechblock thereof rotated to the unlatched position;

Fig. 4 illustrates the weapon of Figs. v1-'23 with its'breechblockwithdrawn from the chamber and swung downwardly on a supportinghinge; Fig. 5 is a. rear view of the weaponof Figs. 1 and 4 with thebreech bar thereof horizontal and the breech block secured within thechamber where it constitutes the inner wall of anannular orifice;

Fig. 6 is a section on line 6-6 of Fig. 5 showing the internalconstruction of our improved weapons barrel, chamber, breech, hingemounting, ammunition. and firing mechanism;

Fig. 7 is a section on line 1-1 of Figure 4, Fig. 4

showing details of the breech block and trigger handle when in the openbreech position;

Fig. 8 is a section on line 8--8 of Fig. 5 showing further details ofthe breechk block, locking devices therefor, the rlng mechanism, andtrigger linkage;

Fig. 9 is a section on line 9-9 of Fig. 5 through the chamber, breechblock,'orifice cone, and cartridge case extractor;

Fig. 10 is a section on line l-IO of Fig. 5 through hinge and'breech barrollers by which the firing mechanism's hammer is cocked upon eachunlatching of the breech;

Fig. 1l shows further detalls of the breech block supporting hinge; Y ln Figs. 12-13 are Aenlarged showings of open and "closed" breech lockswith which the weapon is provided;

Fig. 14 shows the weapons orifice adjusting cone in rear elevation;

that permits quicker clined to the Fig. 15 is a section on line |5-I5 ofFig. 14 through thatcone:

Fig. 16 vshows the hinge xture of Fig. 11 in front side perspective andwith its hammer rollers in place;

Fig. 17 is an enlarged reproduction of the hammer and cooking rollermechanism ilrst illustrated by F18. 10:

Fig. 18 is a perspective showing of the hammer and attached firing pinas they appear when removed from the weapon;

Figs. 19-20-21--22-23 are views illustrative of how cocking of thehammer is effected by each unlatching rotation of the breech bar;

Fig. 24 is an enlarged section on line 24--24 of Fig. 8 through the gunstrigger handle with the trigger and associated safety mechanismin placetherein; and

Fig. 25 is an enlarged perspective view of the trigger and cooperatingsafety mechanism as same appear when withdrawn from the trigger handle.

THE COIVLPLETE RECOILLESS GUN Our inventive improvements are hereillustratively disclosed as being incorporated in a military weapon of75 millimeter caliber capable of a completely recoilless firing ofprojectiles weighing up to 15 pounds at muzzle velocities of 1000! feetper second. This guns overall length is less than 82.0 inches and itstotal weight is but slightly more than 100 pounds. It is designed forconvenient carrying by two or four men and when supported from a lighttripod of the character shown in dotted outline at 29 in Fig. 1 may withcomplete safety to the user be fired with great accuracy and highmilitary effectiveness.

As the description proceeds, it will become apparent that ourimprovements may also be applied to firearms of characters, sizes, andshapes other than the one here disclosed, and that the represented 75mm. open breech weapon thus has been chosen only to illustrate and notto limit the inherently wide application and scope by which theseimprovements are characterized.

The illustrative recoilless firearm here shown consists of a barrel 30;an enlarged chamber 3| secured to the rear of this barrel and having theuniquely tapered shape represented; a breech block 33 partially closing(see Fig. 2) the rear of the chamber; a breech bar 34 secured to theblock and carrying trigger and breech handles 35-36; a pair of carryinghandles 31-38 (see Figs. 1 and 4) and a sight 39I for aiming the gun inconventional manner.

This sight 39 may be of a "direct telescopic type (as shown) or anindirect or other type capable of providing for all iirings within theguns range. It may be mounted on the gun's barrel in any suitablemanner, as sufficiently inleft (see Fig. 1) to make aiming moreconvenient.

As here represented the carrying handles 31-38 are suitably clamped tothe barrel 30 at the intermediate location best shown by Fig. 1. Thesehandles, in conjunction with the trigger and breech handles 35-36 (seeFig. 4) enable two or four men readily to carry the weapon from locationto location.

Once set up on its light tripod 29 (here indicated as being of standarddesign for caliber .30 machine guns of military type), firing of theweapon is controlled by trigger handle 35 conveniently grasped by theright hand of the user who places himself on the left side of theweapon.4 ahead of the weapons breech and in position to look through sight I9in training the gun on its target.

Ammunition having our novel perforated cartridge case form shown atlll-4| in each of Figs. 2 and 6 is loaded into the weapon from thebreech thereof in a manner presently to be explained. Such loading maybe done either by the man who fires the weapon or by an assistant.

THE GUNS RIFLED BARREL As here shown the guns barrel has an insidediameter of 75 mm. (approximately 2.95 inches). a bore area of slightlyless than 7.00 square inches, and a total length of 65 inches. It isconstructed of steel of modified SAE 4340 grade having a minimum yieldstrength of 150,000 pounds per square inch. Its maximum wall ratio(outside to inside radius of the tube) is 1.17 and its maximum wallthickness thus is one fourth inch. A barrel of this material and designwill withstand with a safety factor of over 2 the maximum internalpressure which a firing of the represented weapon sets up.

The bore of this barrel is rifled to secure the usual gains in accuracyand range which a spinning of the projectile in flight makes possible.The rifiing represented has a right hand twist of one turn in 22calibers (or approximately 65 inches of barrel 30) and utilizes thetwenty-eight lands 42 with intervening grooves 43 which Figs. 2 and 6show. Depending upon projectile stability needs other steepnesses oftwist may obviously be chosen; and twists in the left hand direction mayalso be employed with equal effectiveness.

THE GUNS TAPERED CHAMBER As here shown the guns chamber 3| takes theform of an enlarged cylinder uniquely tapered at its forward end andthere aiiixed to the rear of barrel 30 in any integrally secure manneras by the aid of screw threads 44 (see Fig. 6)

'In our improved 75 mm. weapon.here shown this chamber 3| tapers from aninternal diameter of about 3.00 inches at its forward Ajunction withbarrel 30 to about 6.50 inches within its enlarged and untapered rearportion. This latter diameter is considerably greater than the 75 mm,(approximately 2.95 inches) bore of the weapons barrel. The chamberstotal overall length is slightly over 16.0 inches; the enlarged rearwalls thereof continue parallel for 5.35 inches of chamber length; theserear walls have a thickness of 0.62 inch the forward walls of thechamber taper through a chamber length of 8.37 inches; and the insidesurface of each of these forward walls has a taper angle (see Figs. 2and 6) of 10 as measured from the weapons center line.

This uniquely tapered chamber is constructed of steel of modified SAE4340 grade having a minimum yield strength of 135,000 pounds per squareinch. The chamber's internal volume between the breech block 33 and thebarrels end is of the order of 286 cubic inches. Like the barrel, thischamber will withstand with a safety factor of more than 2 any internalpressure likely to be generated during firing.

THE BREECH BLOCK AND CHAMBER ORIFICE As here shown, the guns breechblock is removably secured within the rear of chamber 3|, andconstitutes only a partial closure therefor (see Figs. 2, 9-10) It takesthe form of a cylindrical block 33 which is radially spaced from thechamber wall in a manner to form a substantially block k33 and interfltwith mating protrusions 50 (again see Figs. 3-4` '5) on the chamber wallinterior. Each locking lug 49 carries threads on the periphery thereofas best shown in Fig. 4 and each mating protrusion 50 is provided withsimilar threads indicatedat 5I in each of Figs. 6 and 8.

When these two sets of threads are engaged as in Figs. 1, 5-6 and 8,they securely lock the breech block 33 within the rear of the chamber.

The chamber wall spaces whichcircumferentially separate the lockingrprotrusions 50 have a diameter larger than the maximum for the breechlugs I9' and this relation enables free longitudinal movement by theselugs through the spaces named. This movement is utilized in insertingthevbreech block within the chamber and also in withdrawingvthe blocktherefrom, all in a manner presently to be described.

When inserted and locked within the chamber 3l as shown in Figs. 1, 5-6,and 8 this breech block 33 constitutes a firm support for the ammunitionwhich it helps to position Within the weapon. The steel of its centralcore structure is of suflcient thickness and strength to withstand witha factor of safety of well over 2 the maximum rearward thrust exertedthereon during firing.

A' 'I'I-l'i'.` COMPETE ROUND AMMUNITION 4| and firmly supported withinthe enlarged chamber 3| by the barrel at the forward end and by thebreech block 33 plus an orifice adjusting cone 54 at therear; a quantityof propellent pow-l der r55 within the cartridge case; and powderigniting means shown in the form of a primer 56 anda booster 51.

` This illustrated completev round for the 'z5 mm.

weapon now being described has an overall length of nearly 24 inches anda total weight of about 22 pounds. Of this total weight approximatelyfifteen pounds are in the projectile Il,

about three pounds vin the propellent powder 55,

and about four pounds in the metal case I0.

CARTRmGE CASEv or' coNVEN'rIoNAL SHAPE v v The cartridge case 4o of thisillustrated ammunition round has the same dimensions and contour as docases that are used in one well known the rear oi barrel l0 at the same10' angle as does the guns chamber Il; it then assumesl thesubstantially constant diameter with the exceedingly slow taper kshownin spaced relation to the vwalls of chamber 3lk therearound. The casestotal length is 16 inches and the interior thereof affords approximately138 cubic inches of powder space. The casewall isof durable metal suchas heat-treated steel of modiiied SAE 1030 grade whichis of sumci'entthickness to remain intact during firing. For the '15 mm. case shown a'wall thickness of theorder of 0.070 inch is found to be adequate forthe purpose named. c

i CARTRIDGE cAsE pnarommons AND nmmci` Perforating this wall metal inthe manner tought by our earlier mentioned co-pending application SerialNo. 536,590 are a large number of relatively small openings 60distributed throughout substantially the entire length and circumferenceof the case inthe uniform manner indicated by Figs, 2 and 6. In theillustrative case shown the number of these openings totals 992 and eachhas a diameter of one quarter inch. These case wall openings 50constitute an aggre gate area of approximately 48 square inches ornearly one third of the total surface.area`(about 135 square inches) ofthe represented cartridge case 40. This aggregate opening area is aboutseven times the guns earlier stated bore area of approximately '7.00square inches.

vFor preventing the propellent powder from falling out of these openingsduring loading and for acting as a diaphragm capable of withstandingadequate pressures before rupturing, use is made of a thin layeroffrangible material Il placed inside the perforated case 40 between thecasewall and the powder; In practice one thickness of 0.006 inchlacquered "krait paper constitutes a satisfactory inner wall lining forthe case. Such a lining disintegrates early in the combustion cycle ofthe propellent powder and thus enables escape `of combustion gases andburning powder radiallyA through the openings and into the chamber spaceimmediately surthe metal between wall openings or other damage to thecase. Such security against failure of this kind safeguards the breechorice 4l against blocking by case metal or other obstructions whichwould violently upset recoil neutralization, and allow dangerously highpressures to build up.

THE AMMUNIIIONS PROPIELLENT POWDER The propellent powder represented at55 substantially lls the entire volume of the cartridge case interiorthat is behind a forward retaining disc shown at 62 in Fig. 6.

For the '75 mm. ammunition shown this powder 55 may satisfactorily beused in a quantity totalling approximately 3.00 pounds. satisfactorilyit may be either of a double base" or a single base propellent type. f

One satisfactory grade of double base" composition is identified asP11429 vand includes nearly '79% of nitrocellulose, about 20%nitroglycerin, about 1% Vdiphenylamine, plus small percentages ofinorganic salts. That powders grains may satisfactorily takethe form ofmultiperforated (single perforated are also useable) 7 cylinders about0.5 inch long and about 0.2 inch in diameter and having an average webthickness of about 0.04 inch.

When placed in the quantity stated within the cartridge case this doublebasepowder has a loading density (ratio of powder weight to weight ofvolume of water suicient to nll the case when empty) of the relativelyhigh order of about 0.6. After ignition and expansion of the burningpowder into the total chamber volume (about 286 cubic inches) theapplicable density reduces to the much lower order of about 0.3. Thischange occurs early in the combustion cycle.

The named PL429 powder is found to exhibit satisfactory burningcharacteristics at the relatively moderate pressures employed byrecoilless guns of the illustrated 75 mm. type here disclosed.Typically, such pressures for the particular weapon shown may be of theorder of 10,000 pounds per square inch or less.

POWDER IGNITIN G NIEANS For igniting the propellent charge use may bemade of any suitable primer such as shown at 56-51 in Fig. 6. 'Ihepercussion element 56 of this primer may be of a standard type such asis used in artillery ammunition of conventional design. It serves toignite a larger charge of booster explosive 58 in tube 51 whichsatisfactorily may take the form of black powder in a quantity of theorder of 60 grams. This booster charge is distributed throughout theentire length of the elongated tube 51 and through the representedperforations 59 therein combustion of the CASE POSITIONIN G MEANS In theloaded position shown by Figs. 2, 6, and 9 this cartridge case head 63is positioned centrally with respect to the Walls of chamber 3|therearound. Such central positioning is eifected by the orice cone 54constituting the represented open ring through which the projectile 4|and cartridge case 40 are inserted in loading the 'weapon The breechblock 33, moreover, has a mating recess |30 in the front thereof whichfurther receives the cartridge case head 63 during loading, and uponlocking of the breech in position (as shown in Figs. 6 and 9) abutsagainst the case head thereby restraining same against backwardmovement.

A similar central positioning of the forward end of the cartridge caseis eifected by protrusion of an extreme front section 64 thereof (seeFig. 6) into the bore of barrel 30. Just back of this barrels end thecase 40 flares outwardly as shown in Figs. 2 and 6 at the same 10 wallangle as dr'ies the tapered wall of the weapons chamber 3 The cartridgecase is restrained against longitudinal movement in the forwarddirection by engagement of case head 63's rim with the rear inner edgeof breech cone 54. Such restraint assures that the primer 56 will at alltimes be held registration with the barrels therein by a conventionalcrimped connection which permits ready forward release of the pro.

jectile upon combustion of the propellent powder.

" THE PRE-ENGRAVED PROJECTILE The represented projectile 4| makes use ofa rotating band shown at 68 in Figs. 2 and 6. This band is pre-engraved,in the manner shown by our earlier mentioned co-pending applicationSerial No. 536,590, to assure more ready passage of the projectilethrough the barrel 30s rified bore.

For the 75 mm. ammunition here described, the band 68 may satisfactorilybe made of brass or other metal (such as gilding) about one half inchwide and the pre-engraving thereof preferably is dimensioned to providewith the barrels rifling a diametrical clearance of the close order ofabout 0.005 inch. Clearances of this order assure proper riing; preventobjectionable yaw of the projectile while within the bore and at theinstant of leaving the gun; and at the same time permit the desired freepassage of the projectile through the rifled bore upon combustion of thepropellent charge.

As our co-pending application Serial No. 536,590 more fully brings out,such free passage is exceedingly important for were the projectile tojam, the rearwardly emanating combustion gases then would exert theirfull forward force upon the weapon itself and bodily propel it forwardlyas a rocket. Moreover, such pre-engraving is found to raise the weaponsoverall eiiciency by lowering the force needed to advance the projectilethrough the barrel; it makes complete recoil neutralization relativelymore easy due to cancellation of relatively small forces from which thetypically variable "cutting" component has been eliminated; and theresultant eliminations of engraving pressure behind the projectile andof attendant swedging erosion of the bores lands makes possiblereductions in barrel weight and increases in barrel operating life.

INTERNAL CONSTRUCTION OF PROJECTILE I'his illustrative projectile 4| hasbeen represented as including an internal recess for carrying a quantityof high explosive charge 10 which may be detonated by suitable meanssuch as a time or other fuze (not shown) installed in the projectilesnose 69 (or base) in well known manner. Optionally, thev projectilemight also consist of a solid mass of metal and in that event theillustrated recess for high explosive would be dispensed with.

In either case, the axial and transverse moments of inertia and thedistance from the nose to the projectiles center of gravity will be socoordinated with the firing velocity and barrel rifling as to assurestability during flight. Yaw observations made and other firing dataobtained 'by us confirm that the 15 pound projectile here shown at 4|is. in fact stable when med from the illustrated-barrel 30 having therepresented rifiing twist of one turn in 22 calibers. c

THE ANNULAR ORIEICE AND RECOIL NEUTRALIZATION The 75 mm. recoillessfirearm' illustratively here shown eieci's recoil neutralization in thel unique manner taught by our earlier mentioned co-pending applicationSerialy No. 536,590; that is, the forces of rearward reaction areneutralized the forwardly acting pressure forces acting on the smallannular forward portion of the chamber 3|, the forwardly acting dragforces of the projectile 4| in the ried barrel 30 and by the forwardlyacting force component produced by the pressure of expanding gases inthe conical and divergent portions of the earlier indicated annularorifice 48 (see'Flgs. 2910)'betwe`en the guns breech block 33 and therear wall of chamber 3i wherein ,this block is secured.

As is most clearly illustrated byFigs. 1, 3 -e4-5 this annular oriceextends all of the way around that block's central core and isobstructed only by the four radial lugs 49 which engage with the fourmating protrusions 50 of chamber 3|. All circumferential space betweentheselugs thus constitutes the named annular orice 48 which leads fromthe interior of chamber 3l rearwardly to the exterior of the gun.

Upon ignition of the propellant powder 55 and the resultant discharge.of projectile 4I out of barrel 30 there is expelled through theperforabreech design all ci the nozzle or Venturi" angle is on theinward portions of the annular orificey 48. This serves two usefulpurposes: (a) the major portion of the forwardly acting forces from theexpanding combustionA gases are exerted on the breech block 33 itself,thereby permitting a lighter yconstruction in me parts 49--50 which lockthe block within chamber 3|;'and (b) the resultant inwardly directedVenturi 48 tends to tions 60 of cartridge case 40 combustion gases whichare projected radially against the surrounding chamber wall and thencerearwardly out of the chamber through the annular orifice now beingdescribed. By thus acquiring momen-n tum opposite to that of theforwardly moving projectile the explosive gas thus expelled sets up theaforesaid counterforces which tend to neutralize recoil. y

In our 75 mm. weapon here shown we supplement this momentum eect bymaking the guns annular breech orifice 48 of the represented nozzleshape indicated by Figs. 2, 9 and 10. Starting with a relatively narrowradial width at its front or throat, the annular orifice flares inwardlytoward the rear with an angle of spread of approximately 20 degrees.'Such an angle yields a satisfactory forward force component due to anexpansion of the powder gases in passing rearwardly through the orificeas earlier explained.

Acceptable performance is found to be achieved when the nozzle orificerhas the relatively short length which Figs. 2. 9 and 10 indicate. Thisillustrative length gives a rear discharge or .mouth area of about 12.6square inches which is over two and one-half times the orifices front orthroat area illustratively shown as being of about 4.76 square inches.

represented about 2.50 inches constitute such a length. Dimensions otherthan that shown may of course be utilized with varying degrees of rela-Ativefeiective'ness. f

It will be noted thatin our chamber and In the '75 mm. gun

concentrate the ilring blast into a smaller area, thereby having abeneficial effect on flash ADJUSTMENT Fon zERo REcoIL In our adjustmentfor complete neutralization of recoil we find that there exists anAoptimum ratio between the bore area ofA the guns barrel 30 and thethroat area of the breech orice V48.y

The factors which determine vthe value of this optimum ratio are morecompletely appraised by our earlier mentioned co-pending applicationSerial No. 536,590 which indicates that the required bore-to-throat arearatiov is dependent primarily upon the amount of expansion obtained inthe nozzle 48 and to alesser extent upon such factors as the relativeweights. of the powderand projectile.

In our improved firearm ofthe-illustrative 75 mm, design here disclosedthis ratio for zero recoil is found to lie within the range of fromabout 1.40 to about 160. .Adjustmentl of this ratio to the optimum valuewhich` during. actual firing does in fact produce zero recoil isprovided by theearlier mentioned breechr oriilce cone' 54.

ORIFICE ADJUSTING' CONE In addition to supporting the rear of 'cartridgecase 40, as already described, this coner 54 determines the weaponsratio of bore area itoathroat area. Suchl determination results from`the cones definition of the forward interior wall of the weaponsannular orifice shown at 481by Figs. 2, 9 and 10. As those figuresfurther indicate, the rear interior wall is defined byr the breech block33 when same is secured within the chamber as shown by Figs. 6, 8-9-10.f

While occupying such. a portion of the total orice area as is needed toprovide the necessary adjustment this cone 54 does not alter the basicnozzle shape thereof andv hence it constitutes a particularly efdcientmeans for effecting the required adjustment. The maximum throat area isof course realized when the outside diameter and axial length of cone 54are'relatively small; hence the smallest size of radjusting cone isselected to afford a throat area largeenought to meet the maximumrequirements.

Applying the figures earlier stated, use of such a minimum diameter conemight give arbore-area to throat-area ratio of the 1.40 lower limit. Tovchange this ratio to its other extreme of the named 1.60 maximum it ismerely necessary to install an adjusting cone 54 of sufdciently largerdiameter and axial length as to cut downv the total throat area by therequisite amount;4 and to obtain ratios of intermediate values there'maybe substituted adjusting cones 54k of varying intermediate sizes. i

In practice wend it convenient to markfon each cone the particular valueofbore-to-thro'at area ratio which its use in the weapon -will give.Thus the smallest cone may be marked 1.40; the next larger 1.42; afurther larger size 1.44:l vand so on in increasing increments to thevmaximum cone size of, 1.60. The illustrative cone 'shown in Fig. 14carries thefratio? marking ofl 1.48. The following table lists ratiovalues for the l1 entire range stated, together with dimensions A and Bhaving the signincance best shown by Fig.' 15. Y

Tanta Dimensions of adjustnacone 54 Dimen- Ratio o! Dimen- Bore Area tosion sion Throat Area A" "B Inches Inches From Fig. it will be seen that"A designates the cones outside diameter, while B designates the radiusof the cones rounded forward portion. This radius merges into the conesinwardly tapering outer surface illustratively here shown as dening anangle of degrees with respect to the guns axis. Figs. 9 and 10 show thatthis 20 angle exactly matches the angle of taper by the outer surface ofthe breech behind the cone.

The ratio values set forth by the table are, moreover, based on: (a) a.bore area for barrel 30 of 7.00 square inches; (b) an internal diameterof 6.50 inches for the parallel walled rear portion of chamber 3|; (c) awidth of 1.50 inches for each of the breech block 33's locking lugs 43and the chambers mating protrusions I0; and (d) an inward taper by thecone I4 and the breech block 33 of 20 degrees with respectto the gunsaxis.

Choice of the exact cone size is most eil'ectively determined by trialflrings in a pendulum or other gun suspension which is free to swing andthereby indicate the presence. direction and magnitude of recoil shouldsame exist. In the illustrative '75 mm. weapon represented zero recoilis found to call for an adjusting cone which gives a bore-area tothroat-area ratio of the order-of 1.48. With such adjustment the nozzlethroat has a total area of the order of 4.76 square inches. This isapproximately one tenth of the cartridge cases earlier statedperforation area of about 48 square inches.

SECURING CONE IN CHAMBER In securing the selected adjusting cone 54 inthe chamber position shown by Figs. 3, 6 and 8, we nd it highlysatisfactory to utilize four screws of the type shown at 1| in each ofFigs. 4, 6 and 8. Such screws extend into the four openings indicated atl2 in Figs. 14-15 with similarly tapered extensions of chamber 3 s fourbreech locking protrusions 50. Details of this attachment are best shownby Figs. 4, 6 and 8. The screws 1| are ofthe headless variety havingcountersunk depressions engageable-by a. mating wrench (not shown) fortransmission thereto of appropriate turning torque.

To interchange cones it is only necessary to remove all four of thesescrews 1|, tilt the thus freed con 54 in a way permitting extractingwithdrawal from the chamber-3Is open end as shown in Fig. 4, reinsertthe replacement cone 54 in position within the it by putting screws 1|back in place.

block 33 immediately and thereby hold the cones tapered outer surface inrm abutment chamber and there secure breechs upper portion.

12 vNEUTl'tAlllIZA'I'ION OF ROTATIONAL REACTION As pointed out by ourco-pending application Serial No. 536,590, iirearms with ried barrelsexperience a rotational reaction by virtue of the spinning motion thattiring imparts to the projectile. In the particular gun here shown,barrel 30s right-hand twist gives clockwise rotation (as viewed from therear) to projectile 4| upon forward movement thereof through the barrel,and this right-hand acceleration of the projectiles mass impartscounterclockwise torque of equal magnitude to the barrel.

Our improved 75 mm. weapon here shown includes provision forneutralizing such reactive torque by causing the explosive gases whichrearwardly discharge through the annular breech orifice 48 to impart tothe weapon counterbalanc- 20 zing torque of the same magnitude as thatwhich the rifled barrel imparts to the projectile. This provision iseiiected by so specially shaping the chamber protrusions. that the gasespassing through ,orice 48 have angular momentum imparted thereto.

Each of these chamber protrusions 50 has side walls that are slightlyout of parallel with the guns axis. As Figs. 3-4--5 clearly show, thisside wall arrangement is such that the powder gases flowing rearwardlythrough the oriilce 48 .n

have imparted thereto a counterclockwise rotation (as viewed from therear) these rearwardly moving gases 'being deflected to the right at thelower portion of the breech and to the left at the By reason of thecounteracting spin about the 'guns axis thus given to the gases there isimparted to the chamber 3| a torque counteracting that applied by theprojectile. Only the relatively small degree of angular twist shown isfound suiiicient to make the thus imparted torque of the same magnitudeas the barrel 30 imparts to the 'projectile 4| in advancing it throughthe rifled bore.

All neutralizing torque thus set up by the escaping gases is exerted onthe sides of the lockingr surfaces in the venturi 48 and through chamber3| is transmitted to the barrel 30, and in this way the forces ofrotational reaction are neutralized in a very simple yet highlyeffective manner.

.Were the gun barrel to be riiled with a left-hand twist, rotationalreaction could be neutralized in exactly the same way merely by shapingthe chamber protrusions 50 in the opposite sense.

BREECH BLOCKS WITHDRAWAL FROM CHAMBER Explanation has already been givenof how the breech block 33 is secured in the rear of chamber 3| by theaid of/ that blockslocking lugs 49 and the mating protrusions 50 on thechamber interior. In the engaged position represented by Figs. 1, 5-6, 8this support is all that is needed to hold the breech block in place andit is fully adequate to restrain the maximum chamber pressures whichcombustion of the propellent charge 55 sets up. 4 f

To facilitate loading and removal of the cartridge case 40 after iiring,provision is made for releasing this breech block 33 from its chamberattachment, rearwardly withdrawing'it from the chamber 3| and swingingit out of alignment with the chamber interior to the downward positionshown by Figs. 4 and 7. The earlier mentioned breech bar 34 to which theforwardly extending anali:

13' handles 33-38 are affixed comes into play during these actions. v

Then also utilized is a hinge support tixture 13 having its upper endconnected with breech block 33's center and its lower end connectedthrough a hinge pin 80 and an attachment block 'I8 to chamber 3 I 'slower side wall. Through these elements the breech block 33 continuesto'receive support from the gun after it has been withdrawn from thechamber.

The earlier mentioned breech bar 34 is secured to the breech block 33 bymeans of four bolts shown at I1-in Figs; 3 and 5. Intermediate this barand the main body of the block is an 'o iiset ring-like extension 13 ofthe hinge xture 13. Around this ring extension Vboth the breech block 33and the bar 34 may be turned between the horizontal bar position ofFigs. land and the inclined bar position of Figs. 3 4. In the gun hereshown the range of this angular movement is of the order of 45 degrees,as contrast of Figs. 3 and 5 will indicate.

counterclockwise rotation of the weapon's breech bar 34 serves to engagethe breech locking lugs 49 into the mating threads of chamberprotrusions 58 and thereby securesthe breech block 33 within the chamber3| as earlier explained; clockwise rotation moves the locking lugs outof engagement with the chamber protrusions and into the circumferentialregions between protru- 1 sions. In the latter position, the breechblock 33 is free for rearward withdrawal from the chamber.

Appropriate-limits of such angular travel are established by thoseportions of the hinge support 15 which respectively engage the lowersides of breech bar 34 as shown in Fig. 5 and in Fig. 3. The formerligure shows the bar and breech block 33 at the limit ofcounterclockwise rotation wherein the breech block is securely lockedwithin chamber 3|; the latter .gure shows the bar and block at theclockwise limit of rotational travel in which the block has been freedfor withdrawal fromthe chamber. f

ber 3| as shown in Fig.y 3, the breech block 33 plus bar 34 and handles35-36 are free for rearward withdrawal and downward swinging aroundhinge pin 80 to the position represented by Figs. 4 and '1.

. 14 Purpose of the open" breech lock is to keep the breech block 33 andits attached bar 34 in the y. inclined position of Figs. 3-4 at alltimes except When the breech block 33 is so withdrawn from chamber 3|,the entire interior area. of that chamber is unobstructed vin a waypermitting ready insertion of a projectile 4| and cartridge case 40 intothe gun or ready withdrawal of' a fired cartridge case from the weapon.

To reinsert the breech block into the chamber, it is merely necessary toswing the block upwardly from the position shown in Fig. 4; move itforwardly into the chambers openend as indicated by Fig. 3; and finallygive handles 35--36 and barv 34 a turning movement which bringsv theblock to its counterclockwise limit of rotation in which the lockinglugs 49 thereof engage the chambers mating protrusions 50 as shown inFig; 5.

THE OPEW BREECH noCK vices will be spoken of as the open breech lock.

and the second as the "closed" Abreech lock. 1

when the block is fully inserted into thel guns chamber 3|. This lockthus serves to hold the bar 34 and the breech block 33 in the inclinedposition of Fig. 3 as long as the breech block remains withdrawn fromthe chamber, as in Fig. 4.

in Fig. 7; and a leaf spring 85 beneath the bar 82 in hinge slot 83 asshown in Figs. 6--7 which urges that bar towards the breech block. t

As long as the breech block 33 is fully inserted into the chamber 3|,the bar 82 is held completely within the hinge slot 83 (see Fig. 16) bycontact of thev forward face of the bar with the rear face of thechambers lower protrusion 50 (see Fig. 4). This condition is shown byFig. V6. Under it the bar 82 is completely withdrawn from engagementwith the breech block slot 84 (see Fig. 5) and no rotative restraint isimparted thereby to the breech block. In so far as bar 82 is concerned,the breech block 33 may now be rotated throughout its complete range oftravel.

Once, however, the breech block 33 is withdrawn from chamber 3|, leafspring 85 then pushes bar 82 into the breech block slot 84 as soon asthat slot is brought into alignment with the bar. From Figs. 3 and 4 itwill be seen that such alignment is effected when the breech block .isrotated to the fully unlatched position which Fig. 3 shows. In thatposition the bar moves forwardly into the breech block slot as indicatedby Fig. 7.

Such movement locks the breech block 33 against rotational movement withrespect to hinge mounting 15, in the forward slot 83 (see Fig. 16)` ofwhich the bar 82 is carried. Such locking action continues as long asthebreech is withdrawn from the chamber. It prevents, for example, the

, handles 35-36 and the breech bar 34 from being moved out of theinclined position which Figs. 3-4, and "I represent. Such prevention ismade especially desirable by certain operating char-V l acteristicsof'our unique ring mechanism later to be described.

Upon reinsertion of breech block 33 into the chamber 3|. locking bar' 82is once again'pressed 34 from the disengaged position vvof Fig. 3 tothe' chamber-engaged position of Fig. 5.

THE CLOSED BREECH LOCK becomes effective to hold the breech block 33 in*this horizontal bar position of Fig. 5 until after the weapons firingpin 63 moves forward.. Mechf anism utilizedk includes a closed lockingpin and bar combination 88-89 shaped as shown in Fig. 13 and assembledwith the breech block 33 and breech bar 3 4v as shown by Fig. 8; a slotout into the right side of hinge ring 'I9 as shown in Figs. 8 and 11 tobe engaged by locking bar 88 as indicated by Figs. 5 and 8; a spring 8|which l urges the rear of bar 89 into hinge slot 99 as indicated by Fig.8; and a firing mechanism hammer 92 having on its side wall a groove |98(Figs. 18-19) whose bottom is tapered sofas conveniently to engage anend of bar 89 in the manner also shown by Fig. 8.

This hammer 92 is carried Within a hollow case 93 which is integral withand extends back from the breech bar 34 inthe manner indicated by Figs.1 through 10 and 17. As will later be explained, this hammer is movedrearwardly to the"cocked" position shown by Figs. 6-7-8-9y upon eachunlatching rotation of breech bar 34; and it is released .for forwardadvancement to the fired" position shown by Figs. and 17 upon eachdepression of the guns trigger 94 in handle 35.

As long as hammer 92 is cocked, the taper of groove |96 in the side wallthereof indicated by Fig. 8 allows spring 9| to force locking bar 89inwardly into engagement with hinge ring slot 99 (see Figs. 8 and 11)and thereby restrain the breech block and its bar 34 from rotativemovement with respect to the hinge. This assures that the breech barmust remain in its chamberengaged position of Fig. 5 unless either thehammer 92 moves forwardly to the position of Fig. 9 or unless lockingpin 88 (see Fig. 5) is manually moved to the right against spring 9|(see Fig. 8).

Upon release of hammer 92 to its forward or fired position of Fig. 10the slow taper of'groove |98 in that hammers side wall wedges bar 89outwardly against spring 9| and thereby moves that locking bar out ofthe hinge rings slot 99 (see Fig. 11) This wedging action imposes suchsmall restraint upon forward movement of the hammer that it in no wayinterferes with the desired operation of our weapons firing mechanism. Yl

Each iiring of the weapon therefore automatically unlatches the breechblocks closed locking bar 89 and frees the breech block 33 for clock@wise rotation and subsequent withdrawal from chamber 3 I 'Ihis resultoccurs whether ammunition is or is not present in the weapon.

A similar release of the "closed breech lock may be eiected manually asearlier mentioned. Such manual actuation requires only that the lockingpin shown at 88 in Figs. 3 and 5 be pushed to the right against spring 9I of Fig. 8. Such pushing releases the breech block forclockwise-rotation and withdrawal out of the chamber even though theweapons hammer 92 maybe cocked as indicated by Figs. 6-7-8-9.

'.IHE FIRING MECHANISM For igniting the ammunitions propellent charge 55at the will of an operator use'may be made of any suitable firingmechanism. Here represented by way of illustration is a uniquemechanical type of firing mechanism by the aid of'which an operator mayfire the weapon by l a simple depressing of the earlier mentionedtrigger 94 carried by handle 35.

In the disclosed arrangement the firing pin 86 carried by the gunsbreech block 33 receives through direct attachment with the earliermentioned hammer 92 a ring blow created by the forward movement of thathammer. The force incident to that forward movement originates in acompression spring 91 c'arried between the hammer92 and case 93 as mostclearly shown in Fig. 17. This force is made available for firing thegun when a sear shown at 98 in Fig. 8 is withdrawn from in front of thehammer.

The illustrated hammer 92 takes the form of 16 a metal cylinder havingthe general appearance best indicated by Fig. 18. The ring pin 84 isscrewed into the front of this cylinder and thus at all times moves inunison therewith. This movement is between the oocked" position of Figs.6-7-8-9 and the fired" position of Figs. 10 and 17.

cocmNG or 'rmt HAMMER As earlier stated. cocking of the hammer from theforward position of Figs. 10 and 17 to the rearward position of theearlier named gres is eii'ected by rotation of the breech block 33 andits bar 3 4 from the horizontal bar" position of Fig. 5 to the inclinedbar" position of Fig. 3. Such rotation is translated into rearwardmovement of the hammer by means of two pairs of rollers shown at |99 andat lll in each of Figs. 19. 16-17, 19-20-21-22v-23.

Rollers |39 are carried by the hinge ring 19 (see Figs. 10, 16`17),while rollers lll are carried by the breech bar 34. Both sets of thenamed rollers engage with longitudinal slots |93 in the outer surface ofhammer 92. The forward portion of each of these slots is tapered asshown at |94 in Figs. 17-18-1920, 22-23.

With the breech bar 34 in the horizontal position of Fig. 5 both sets ofthese rollers lill-|91 lie along line |9-Il of Fig. 5, and sectionstherethrough appear as shown in Figs'. 10and 17. The hammer 92 is shownby Figs. 10 and 17 and 22 in itsA forward or ilred position whereinfiring pin 66 has by the hammer and compression spring 91 been moved toits forward limit of travel.

Upon rotation of the breech bar 34 from the horizontal position of Fig.5 to the inclined bar position of Fig. 3 the forward or hinge rollers|99 remain stationary, while the rearward or bar rollers |9| rotate thehammer clockwise as viewed from the rear, from the position shown inFig. 20 to that indicated by Fig. 21, an angular rotation ofapproximately 26.5 degrees. Fig. 20 will be seen to correspond to Fig.19, except that Fig. 19 shows the hammer and its rollers as viewed fromthe front or right of Fig. 17.

The named rotative movement brings the tapered sides |94 of the hammerslots |93 against stationary rollers III, and by a camming action bestapparent from Figs. 18 and 22 forces the hammer 92 backward againstcompression spring 91 and into the cocked position shown by Figs. 21 and23 as well as by Figs. 6-7.-89. When the cocked position has beenreached the sear shown at 98 in Fig. 8 is by spring action later to bedescribed forced inwardly ahead of the rear face of a restraining slotshown at |49 in Figs. 8, 19, 22 and 23. f

RELEASE OF THE HAMMER In this position the sear 98 holds the hammercocked until such time as trigger 94 may be depressed. Upon suchdepression of the trigger the sear is withdrawn from its engagement withthe restraining slot |49. and hammer 92 plus ring pin 66 are allowedtomove forward due to the expansive force of spring 91. 'Ihis forwardmovement brings firing pin 86 against the ammunitions primer 98 (seeFigs. 6 and 9) and thereby fires the weapon.

The named forward movement can, of course, take place only after thebreech bar 34 has been returned to the horizontal position of Fig. 5. Inthat horizontal position bar rollers |9| are again realigned with hingerollers |99 as shown in Figs. 10, 17, 19-20, 22. 'I'his realignmentfrees the hinge rollers |99 t6 cam the hammer 92 backhammer forunrestrained forward movement as soon as sear 9| is withdrawn from thefront of the Y latching slot |40 therein. *In the illustrativeconstruction shown hammer K it will not restain longitudinal movement ofthe COMPLETE HAMMER OPERATION The just described hammer mechanism willthus be seen to operate vas follows. Following each firing' of theweaponthe firing'pin 66 and hammer 92 occupy their forward positions asshown by Figs. 10 and i7 while the breech block 33 is still locked inchamber 3| with the bar 34 horizontal as shown in Figs. 1 and 5.

Rotation of the breech bar 34 to the inclined position shown in Fig. 3causes the bar rollers |9| to rotate the hammer 92 clockwise as viewedAfrom the rear, and this action in turn causes wardly against compressionspring 91 as already explained .by reference to Figs. 17 through 23.

The so-cocked hammer now occupies the position shown-by Figs. 6-7-9-9and 23. Retention in that position is eHected by sear 98 blockingforward movement of the hammer as shown by Fig. 8.

This blocking continues vduring subsequent withdrawal of the breechblock 39 from the chamber to the position shown by Figs. 4 and 7. Italso remains eiective during reinsertion of the breech block into thechamber and engagement therewith by restoration of breech bar 34 to thehorizontal position of Fig. 4. Such` restoration re-aligns rollers ||0|from the condition shown by Fig. 21 to that indicated by Fig. 20.

Thisdre-alignment conditions the hammer for subsequent forward movementupon withdrawal of the restraining sear 98. Upon such withdrawal spring91 forces the hammer and its firing pin 66 rapidly forward into contactwith the cari tridge cases primer 56 and thereby detonates the primerand fires the weapon.

By this action the iring mechanism is returned 55 projections He.,Following insertion of theparts zgihegfn :gefrmg condition with which ofFig. 25 into the trigger handle 35 the triggers n safety buttons opposedlower projections |`|4 (see THE 'I'RIGGER AND SAFETY Figs. 24 and 25)fit into an annular gl'OOVe l5 that MECHANISMS l extends completelyaround the trigger handles Cooperating with the hammer 92 and its justdescribed cooking mechanism are trigger and safety mechanisms which willnow be explained.

These utilize the earlier mentioned s ear shown at 99 in Fig-8; theearlier mentioned trigger shown at 94 in the same figure asprotrudingfrom the y forward end of trigger handle 35; and a rotatable vsafety button `|09 carried in the hollow end of that Y handle as alsoshown by Fig. 8.

The sear 93 takes the Vform of around rod l 4smartly housed intheleftlhalf of breech bar 34 70 betweenthe rear wall of that bar and avfront cover plate |09 `and having an outer end which is inclinedAasshown by Fig. 8 into a mating opening in the inner end of theplungerflike trigger 94...Y Thistrigger is 'axiallymove'able within han-75 ale u and safety mure m but is by a rey I| n j H4; however, theintervening agency of thek .spring `Il l, being connected to the safetybutton below the projections ||4 and also connected .to trigger 94,limits such travel to the distance over which spring I I9 may becompressed against projections ||4.v Such Vurging holds sear 98 againsthammer 92 as shown byFig. 8. Y. Reference to Fig. 25 shows that springH0 not only exerts tension between parts 94 and |09 but that it also isarranged to impart turning `effort on safety button |99 with respect totrigger |09. as will be more fully explained below. Incident to thisturning eilort use is made of thekey which passes through an opening inthe trigger 94 and by engagement with longitudinal slots H2 inside thetrigger 'handle-35 (see vFig. 24) prevents rotation of the triggerwithin that handle while at the same time permitting axial triggermovement withrespectto the handle.

4Safety button |99 is provided with side slots through which the ends oftrigger key lll protrude as shown by Fig. 25. The trigger spring ||9encircles the trigger rod 95 as that figure also shows. The two ends ofthis spring respectively are attached: (a) to an enlarged portionof thatrod shown inlligs. 8 and 25. at/the searengaging end thereof; and (b) tothe inner end of the safety xture |99 (again see Fig. 25)

During assembly ofthe parts shownin Fig. 25

this spring is so wound onto its two end attachrments thatupon insertionof the trigger key lil through the safety slots and the trigger, the

urge positions the safety slots as shown in Fig. 25 y and therebysafeguards the trigger 94 against accidental depression into the gunshandle 35.

To insert the safety mechanism of Fig. 25 into the trigger handle 35 thetrigger 94 in relation to the safety |99 isdepressed and rotatedto itsfullest extent so as yto align key ill' with the 94 is free only foraxial movement through the.

handle and fixture.

'CONDITIONINGA THE SAFETY Fon- FIRING n It has now beenv seen thattriggerspring ||0 urges the scar-end of trigger 94 outwardly towardthesafety |39 and at the same timeurges button |99c1ockwise (see Figs. 4and 25) with respect to the trigger and pin I extending therethrough.These two actions respectively hold the sear 99 against the gunshammer92 andfmain- Under this condition'the tain the side slots ofsafety |09 in the position of Fig. 25 to restrain inward movement of thetrigger.

The rotational force .on the safety button |09 at all times assists thetension force of the trigger spring I| in forcing the sear 98 inwardlytowards the hammer 92. This is accomplished by the cam surfaces of theside slots in the safetyv button |09 (see Fig. 25) engaging with thetrigger key I I I. This essentiallyhas the effect of retaining the searin position by a wedge-like action to make its operation more positive.

In order to condition the weapon for firing it is only necessary to turnthe safety button |09 counterclockwise as viewed in Fig. through anangle of about 45. Such turning removes the slot side walls of fixture I09 from the path of inward travel by trigger key III. Depressing forcenow applied to trigger 94 results in inward movement thereof which pullsthe sear 98 ofFig. 8 outwardly away from hammer 92 and thereby releasessame for forward firing movement under the action of compression spring91.

ASuch firing of the weapon, moreover, is possible only when safety |09is held in the counterclockwise turned position against the clockwiserestoring torque of spring I I 0. Under this ccndition the trigger 94may be depressed as just described. Under all other conditions spring II0 holds safety |09 in the position of Fig. 25 Wherein depression of thetrigger and firing of the Weapon are effectively prevented. 1

LOADING AND FIRING From the foregoing it will be seen that we haveprovided an improved recoilless firearm which offers importantadvantages in connection 4with both loading and firing. To place theammunition round within the weapon it is merely necessary to unlock thebreech block 33. withdraw it from the chamber 3| and swing it downwardlyto the position shown by Figs. 4 and 7 thus completely freeing thechamber opening.

The ammunition round 40-4I is now inserted into the opened chamber andthe rear of the barrels bore. As the projectile enters the barrel thelands on the pre-engraved band 68 are brought into alignment with thegrooves of the barrel bore and forward thrust is then continued untilthe rim of the cartridge case head 63 abuts with the breech cone 54. Inthis position the forward end of the cartridge case is centered by thebarrel and the case head 63 is similarly centered within the chamber 3|by the breech cone 54 therearound. The breech block 33 (together withbar 34 and handles 35-36) is now moved upwardly and forwardly into thechamber. In approaching and engaging with the cartridge case head 63 theflared recess |30 in the breech blocks front comes the hammer and firingpin 66 to cause detonation of percussion element 56 and ignition ofprimer and propellent charges 53 and 55.

The resultant combustion of propellent 55 discharges the projectile 4|and at the same time ruptures the perforated cartridge cases frangiblelining 5I and produces radial expulsion of the explosive gases into thechamber 3|. This expulsion starts early in the burning cycle and isaccompanied by continued combustion of the powder.

The resultant pressure within the chamber produces escape of theexplosive gases through the annular breech orifice 46 and thence to therear of the weapon. As already explained in part, this escape ofexplosive gases sets up counter forces which completely neutralizerecoil and thus permit the weapon to be fired from a light tripod asshown at 29 in Fig. 1 or other suitable support,

The perforated wall metal of cartridge case 40 remains intact duringthis firing and is not ruptured or otherwise damaged. Since expulsion ofexplosive gas from all of the case perforations is simultaneous, therepresented tapered design of chamber 3| is in practical use found to befully eective for diversion of the gases to the rear. The flow from theforward portion of the case adds to that from openings farther back andthus builds up in amanner appearing generally to approximate theincreasing area within the chamber as the cases rear is approached.

Subsequent withdrawal of the fired cartridge case from the chamber ispreceded by rst unlocking the breechblock and then withdrawing thatblock rearwardly and downwardly out of register with the chamber andinto the position on hinge'support 'I5 which Fig. 4 shows. Extraction ofthe red case now becomes possible.

EXTRACTION OF FIRED CASES For facilitating such extraction we supplementour hinge-mounted breech block 33 by an extractor represented at I I Iin each of Figs. 4, 7 and 9. This extractor takes the form of aright-angle piece of metal protruding as shown from the lower face ofthe breech block 33. The position of this protrusion is such that theextractor hooks under the rim of the cartridge case head 63 in themanner shown by Fig. 9 when the breech block is positioned within thechamber.

The interior portion of this extractor lits into a recess in the breechblock metal and is there into abutment with the head and thereby re- 1strains the case against rearward movement.

Counterclockwise rotation of the breech block by bar 34 and handles35-36 now locks that block into the chamber with the case heads rim inabutment with the breech cone 54 and the case head in abutment with thebreech block,

' the primer 56 in alignment withlthe ring pin 66 and the entirecartridge case 40 centrally positioned within the surrounding chamber 3I.

The hammer 92 now has the cocked condition shown by Figs. 6 and 8 andthe weapon is j accordingly ready for ring. Upon the earlier explainedrotation of safety button |'09 a backward pressure on handle 35'strigger 94 will release held by a retainer bar I I8 fastened over therecess by screws'indicated at I|9 in Fig. 4. A compression spring |20urges the extractors lip inwardly toward the center of the breech blockas shown in Fig. 7. Y

Upon insertion of the breech block into the chamber after theammunitions cartridge case 40 has been placed therein, the exposed endof extractor III rst contacts the case head and is by it pushed inwardlyand at the same time outwardly beyond the edge of the case heads rim.Continued advancement of the breech block into abutment with the casehead forces the extractors hooked end into the position shown by Fig. 9.Under this condition the extractor hook is ahead lof the case rim and isurged inwardly thereagainst by compression spring |20.

After firing of the weapon unlocking of the breech block 33 andsubsequent withdrawal thereof from the chamber to the position shown inFig. 7 causes the extractor I1 to pull the fired case from the chamberto a position where the head thereof substantially protrudes from thecham- .Y sequentiiring of another ammunition round;

, 2l j bers open end. 'Ihe limit of this withdrawing movement visdetermined by the pointv at which" the extractor hook H6 is broughtbelow the level of the case rim in turning with the breech block v33faround the hinge pin Il (see Figs. 6 7).

In this position the case can readily begrasped by the user andwithdrawn from the weapon thereby conditioning same for insertion andsubo'rrmi. MECHANICAL Daraus For facilitating assembly and disassemblyof the various parts and mechanisms of our .'15 mm. recoilless weaponwe'have provided fr carriage within the weapons breech handle 36 ofspecial v wrenches (not herevshown) by the aid of which all removableparts of the weapon may be dismantled for cleaning, adjustment orreplacement.

'I'he wrenches mentioned may be of any suitable type useable to: (a)turn the screws 1I by '20.

able head |22 which screws' into the handles threaded open end as shownin Fig. 8.

Carriage of the wrenches in this manner in no f wayy interferes with theintended functioning of 'specifled. Then there fis: -(a) chosen for thecess thereto this handle is provided with a remov- 30 the firearm andallows these highly useful tools conveniently to be kept with the weaponmediate availability at all times.

PERFORMANCE DATA The iiring of thousands of rounds of ammunition hasconfirmed beyond all doubt the successful and practical character of theimproved re. coilless firearm here disclosed. With the representedprojectile 4i weighing 15 pounds, muzzle for imvelocities of 1000 feetper second are consistently attained yby use rof propellant charges ofthe earlier described 3 pounds of PL-129 double-base powder orequivalent (single or double-base) Complete neutralization of recoil isuniformly achieved, and when firing `the weapon from a tripod or otherconvenient support users report a completeabsence of weapon motionbackward, rotative, side'wise, or forward. A

Accuracies of a high order also are achieved.-

At 300 yards it is possible to hit a one-foot bulls eye with remarkableconsistence; at 600 yards the shot pattern is well-defined by athree-foot circle; and at 1000 yards hits can be scored on asixfoot'target. Accuracies of comparable order are realized at evengreater ranges.

The relatively light weight and small dimensions ofthe weapon at oncemake -it possible for infantry use, and place in the hands of individualsoldiers an effective defense and offense against enemy tanks' and othermilitary objectives.

vBALLISTIC DESIGN calculation more fully disclosed by our earlier 70mentioned co-pending application Serial No. 536,590. In view of 'thecomplete explanation presented by that earlier application no VattemptAat repetition will here be made.

' analytical procedure, dimension calculations and c optimum designselection are made in a manner closely similar to that which ourco-pending ap..

plicatlon fully sets forth.y That is to lsay. the projectile-mass,muzzle velocity, caliber, barrel length and gun weight requirements arefirst firearm a breech nozzle of size `and/expansion ratio calculated toeifect recoil balance; (b) 'selected a propellent powder withcomposition', burninng constant and web thickness calculated tovcomplete vcombustion about simultaneously l with the-projectiles'leaving ofthe barrel: (c) assumed a series of flow factor values andcalculated foreach the powder charge, chamber volume,` barrel length,internal pressure and gun weight; and (d) selected for the flrearmthe owf actor whose calculated design values most closely match the specifiedrequirements to be met.

AThe design thus calculated is experimentally verified =by exhaustiveproof iirings land such modications as will improve the weaponsperformance are then made. The resulting recoilless firearm isthoroughly practical andy gives a 25 repower per unit weight which isfar in excess of the best heretofore attainable.

SUMMARY The earlier described qualities of superior recoilless gunperformance are the direct .result of our here disclosed improvements inthe design and construction of open-breech rearms. The individualfeatures of such improvements are numerous and in the complete weaponthese features effect the named results through cooperations andinteractions which are both unique and novel. i

From the foregoing it will thus be seen that We have improved 'thedesignand extended the 0 usefulness of recoilless guns which incorporateprinciples of construction and 'operation first disclosed and claimed byourv co-p'ending application Serial No. 536,590 filed May 20, 1944, forRecoilless firearms, ammunition therefore and ballistic design thereof;that we have provided for such open breech recoilless guns unique weapondesigns and constructions which are peculiarly adapted to iirearms of'75 mm. and other high calibers; that We 'have' provided improvedchamber and breech constructions for recoilless guns which utilize theannular orice" and the "perforated cartridge case principles of ourearlier applications just mentioned: that we have facilitated`adjustment of breech orifice area and the` securing of zero recoil at adesired performance level; that we have increased the sim-y of,wideapplication and hence are not to be re-v stricted to the specicform hereshown and deplicity, ruggedness and compactness of breech actions and offiring and ,safety'mechanlsms for recoilless firearm use; andthat Wehave made possible the practical construction and successful use oflarge caliber recoilless firearms whichare capable of shooting'vprojectiles carrying heavy quantities of explosive through longdistances andv yetv which are so relatively light in weight and socompact in size as to be readily portable.

Our-inventiveimprovements thus are capable scribed by way ofillustration.

We claim: n 1. In a recoilless firearm, kthe combination of a barrel. achamberextending rearwardly from said barrel and having walls whichtaper outwardly through at least half the chambers'length It willsuflicet0 Say 'that the design formula. 75 from the diameter `of said barrels bore at the chambers front to a substantially larger diameter atn thechambers rear. an ammunition round comprising a, projectile positionedin the rear bore of said barrel and a cartridge case positioned withinvsaid chamber communicating. with said projectile and containingpropellent powder, a metal wall for said case forming for said powder a'cylindrical enclosure of diameter approximately the same as saidsurrounding chambers forward end but substantially less than thatchambers enlarged rear portion and being perforated by a latively largenumber of openings distributed circumferentially 'and lengthwise thereofand through which powder combustion gases may expand radially into saidtapered chamber therearound, a breech block secured in the rear of saidchamber and there providing an oriiice which f `leads from the chambersinterior to the rear exterior thereof and which permits escape of powdergases in proper quantity and at proper rate to neutralize recoil, andmeans including said breech block for supporting said perforatedcartridge case against rearward movement and in spaced relation to thesurrounding walls of said tapered chamber.

2. In-a recoilless firearm, the combination of a barrel, a chamberextending rearwardly from said barrel and having walls which taperoutwardly through at least half the chambers length from the diameter ofsaid barrels bore at the chambers front to a substantially largerdiameter at the chambers rear, an ammunition round comprising aprojectile positioned in the rear of said barrel and a cartridge casepositioned containing propellent powder positioned within said chamberand communicating with said projectile, a metal wall for said caseforming for said powder a cylindrical enclosure of diameterapproximately the same as said surrounding chamberss forward end butsubstantially less than that chambers enlarged rear portion and beingperforated by a relatively large number of openings distributedthroughout the circumeference and length thereof, means including abreech block in the rear of said chamber for supporting said cartridgecase against rearward movement and in spaced relation to the saidchamber walls therearound and for also providing a substantially annularorice which leads from the `chambers interior tothe rear exteriorthereof, and means for igniting said powder whereby to form powdercombustion gases that cause the discharge of said projectile forwardlyout of said barrel and that at the same time cause neutralization of theforces of recoil by expulsion of said gases through said case wallopenings radially into said tapered chamber and thence rearwardly out ofsaid orifice.

3. In a non-recoil gun, the combination of a barrel, a chamber extendingrearwardly from Said barrel and having walls which taper outwardlythrough at least half the chambers length from the diameter of saidbarrels bore at the chambers front to a substantially larger diameter atthe chambers rear, an ammunition round comprising a projectilepositioned in the rear bore of said barrel and a cartridge casepositioned within said chamber communicating with said projectile -andcontaining propellent powder, wall metal for said case forming for saidpowder a cylindrical enclosure of diameter approximately the same assaid surrounding chambers forward end but substantially less than thatchambers enlarged rear portion and being perforated by a relativelylarge number of openings distributed throughout 24 the circumference andlength thereof, a layer of frangible material separating said powderfrom and preventing its passage through the case wall perforations priorto nring but yielding to the l gas pressure of powder combustion, abreech block securedv in the rear of said chamber and there providing anorifice which leads from the chambers interior to the rear exteriorthereof and which permits escape of powdergases in proper quantity and aproper rate-to neutralize recoil, and means including said breech blockfor supporting said cartridge case against rearward movement andin\spaced relation to the surrounding walls of said tapered chamber.

4. In, a non-recoil gun, the combination of a barrel, a chamberextending rearwardly from said barrel and having walls which taperoutwardly Y through at least half the chambers length from the diameterof said barrels bore at the chamers front to a substantially largerdiameter at the chambers rear, an ammunition round comprising aprojectile positioned in the rear bore of said barrel and a cylindricalcartridge case of perforated wall metal-communicating with saidprojectile and having Va diameter approximately the same as saidsurrounding chambers forward end but substantiallyV less than thatchambers enlarged rear portion, propellent powder within said perforatedcartridge case, a breech block secured in the rear of said chamber inradially spaced relation to the enlarged diam-eter chamber wallrtherearound and there Iforming with that wall a substantially annularorice which leads from the chambers interior to the rear exteriorthereof and which rearwardly diverges inwardly towards the gun's axiswhereby to converge around that axis powder gases from said cartridgecase vexpelled through the orifice, and means including said breechblock for supporting said cartridge case against rearward movementvchambers length from the diameter of said barrels -bore at the chambersfront to a substantially larger diameter at the chambers rear, anammunition round comprising a projectile positioned in the rear bore ofsaid barrel and a perforated cartridge case 'within said chamberextending at its front into the rear bore of said barrel forcommunication with said projectile and having a body diameter. largerthan that of said bore but substantially less than that of said chambersenlarged rear portion, means in the rear of said chamber for supportingsaid cartridge case against both rearward and forward movement andspacedly positioned with respect to the surrounding chamber walls so asto provide a connecting passageway between the space around the case andthe chambers rear exterior, and tapered walls' at the front of saidcartridge cases body which are angularly mated with the lectilepositioned within the rear of said barrel and a perforated cartridgecase within said chamber extending at its front into the rear bore ofsaid barrel for communication with said projectile and having a bodydiameter substantially less than that of said chambers enlarged rearportion, a rim extending radially from the rear portion of saidcartridge case, a ring xed within the chambers rear portion andencircling said cartridge case immediately ahead of its said rear rimwhereby to restrain thev case-against forward movement andv to supportsame in radially spaced relation to the surrounding rear chamber walls,and a breech block movable into and out ofthe portion of said cham-berthat is behind ,said ring and having a forward face which abuts the.rear portion of said cartridge case and thereby restrains same againstrearwardy movement, said breech block further -providing a connectingpassageway between the space around said cartridge case and the chambersrear exterior.

7. In a non-recoil gun, the combination of -a barrel, a chambercommunicating with said barrel and having a rear diameter substantiallylarger than that of the' barrels bore, an amv v munition roundcomprising a projectile positioned in the rear of said bore and acylindrical cartridge case of `perforated wall metal situated -saidcartridge -case rim and said ring and also in radially spaced relationto the chamber walls therearound whereby to restrain the cartridge caseagainst. rearward movement and to form with the chamberwalls asubstantially annular 'orice leading from the chambers interior pastsaid ring and to the rear exterior of the chamber.

8. In a non-recoil gunfthe combination of al barrel, a chambercommunicating with said barrel and having a rear diameter substantiallylarger than that of the barrelsv bore, a perforated cartridge casewithin said chamber having a cross sectional area substantially lessthan that of said chambers rear portion and being supported at its frontby said barrel, a ring xed within the chambers rear portion inencircling relation to said cartridge case whereby to supportsameagainst lateral movement and being radially spaced from the surroundingchamber wall whereby to form with that wall a substantially. annularorifice whichleads from the chamber interior to the'rear exteriorthereof, and a breech block secured in said chamber behind said ringlikewise in spaced .relation to the aforesaid chamber wall whereby tosupport said cartridge case against rearward movement while at the sametime containing said annular orifice without obstruction.

9. In a recoilless firearm, the combination of a barrel having a borerifled with twist in al given direction, a -chamber secured to the rearof said bore, a propellent charge supported within said chamber inspaced relation to the walls thereof for generating combustion gases bywhich said projectile lis pushed forwardly through said barrel androtated in said given direction bypsaid bore's riding, a breech block inthe rearward portion of said chamber having its periphery cut away atspaced portions circumferentially of the block to provide asubstantially annular orice interrupted by lugs that extendsubstantially radially from the blocks central portion, matingprotrusions extending inwardly from said cham'- bers rear interior intoengagement with said breech .blocks lugs and serving to secure saidblock within the chamber, and side walls for said chamber protrusions'and said breech bl'ock lugs so inclined axially as to receive from saidcombustion gases which pass rearwardly through' said annular orificegiven direction rotative forces' substantially equal to the forces oftwist which Ysaid projectile receives from said riiled barrel.

10. In a non-recoil gun, the combination `of a barrel, a chambercommunicating with said barrel, a breech block movable into and out ofthe rearward portion of said chamber and having its periphery cut awayat spaced portions circumferentially of the block to provide asubstantially annular orifice interrupted by locking lugs that extendsubstantially radially from vthe central portion ofthe block, coactingprotrusions from the chambers inner wall engageable by said locking lugsto secure said block within the chamber, and an orifice area adjustingring xed within said chamber immediately ahead of and concentricallywith respect to said breech block and having an external diametersuillciently larger than that of the breech block at'its said cut awayportions as to reduce the totalv area ofsaid annular orifice by apreselected amount.A i f,

l1. In a non-recoil gun, the combination of a barrel, a chambercommunicating with said barrel, a breech block movable into and out ofthe rearward portion of said chamber and having its periphery cut awayatspaced portions circumferentially of the block to provide anfannular andrearwardly diverging orifice vthat isv interrupted by locking lugsextending radially from the central' portion of the block, coactingprotrusions from lthe chambers'inn'er .cwallfens blockr gageable bysaidlocking lugs lto securesaid within the chamber', and an orifice area ajust'- ing ring of rearwardly converging' contourilxed within saidchamber immediately'ahead, ofrmand` concentrically with respect to said,breech Iblock-..1

and in abutment therewith and having an,

ternal diameter which is larger than that of the I rupted by lockinglugs that extend substantially` radially from the central portion of theblock,

coacting protrusions from the chambers inner wall engageable anddisengageable by said locking lugs upon locking and unlocking rotationsof the breech block within the chamber, a support for said breech blockarlxed to the rear exterior of said chamber in radial alignment with oneof said chambers protrusions. and a hinge member extending radially fromsaid support tol the breech block in line with one of said lugs in theblocks locked position and permitting rotative movement of the blockwithin the chamber plus complete withdrawal therefrom -as well asimparting support to the block when so withdrawn plus guiding action forreinsertion into the chamber. y

13. In a'recoilless firearm, the combination of a barrel, an enlargedchamber extending rearwardly therefrom, a projectile in the rear of saidbarrel, a cylindrical cartridge case of perforated wall metal withinsaid chamber spaced from the rear walls thereof and communicating at itsfront with said projectile, a breech .block movable into and out of therearward portion of said chamber immediately behind said cartridge caseand having its periphery cut away at spaced portions circumferentiallyof the block to provide a substantially annular orliice leading from thechambers interior to the rear exterior thereof and interrupted bylocking lugs that extend substantially radially from the central portionof the block, coacting protrusions from the chambers inner wallengageable by said lugs when the breech block is in a ilrst rotativeposition whereby to secure said block in the chamber and interspacedbetween saidflugs when the breech block is in a second rotative positionwhereby then to free said block for withdrawal from the chamber, and abreech block support member spanning said annular oriilce in line withone of said chamvbers protrusions and pivotally joined with said breech.blocks center whereby to permit block rotation between said first andsecond positions and hingedly joined with said surrounding chambers wallwhereby supportingly to permit complete withdrawal of said block fromthe chamber as well as impart guiding action to the block uponreinsertion thereof into the chamber.

14. In a non-recoil gun, the combination of a barrel, a chambercommunicating therewith, a breech block movable into and out of the rearportion of said chamber and having its periphery cut away at spacedportions circumferentially of the block to provide a substantiallyannular orice interrupted by locking lugs that extend substantiallyradially from the central portion of the block. coacting protnx'sionsfrom the chambers inner wall engageable and disengageable by saidlocking lugs upon locking and unlocking rotations of the breech blockwithin the chamber, a support for said breech block affixed to the rearexterior of said chamber, a hinge member extending radially and in linewith one of said chambers protrusions from said support to the center ofsaid breech block and permitting rotation of the block within thechamber plus supported withdrawal therefrom, a bar extending across andsecured to the rear of said breech block in line with opposing of saidlocking lugs carried by the block, and operating handles extendingforwardly from said 4bars two protruding ends to facilitate turning ofthe breech block within the chamber and to aid withdrawal of the blockfrom and reinsertion of the block into the chamber.,

15. In an open breech recoilless firearm, the combination of a barrel, achamber communicating with said barrel and having a rear diametersubstantially larger than that of the barrels bore, a perforatedcartridge case within said chamber having a cross sectional areasubstantially less than that of said chambers rear portion and beingsupported at its front .by said barrel, a rim extending radially fromthe rear portion of said cartridge case, a ring fixed within saidchambers rear portion and encircling said cartridge case immediatelyahead of its said rear rim whereby to support said case in radiallyspaced relation to the rear chamber walls', a breech block movable intoand out of the rearward portion of said chamber immediately behind saidcartridge case and providing a connecting passageway between the spacearound the cartridge case and the chambers rear exterior, and anextractor xture protruding from the forward face of said breech `blockfor latching engagement over the'rear rim of said cartridge case wherebyupon withdrawal ofthe block from the chamber the cartridge case is atthe same time also partially withdrawn from the rearm.

WILLIAM J. KROEGER. CLARENCE WALTON MUSSER.

REFERENCES CITED The following references are of record in the ille ofthis patent:

UNITED STATES PA'I'ENTS Number. Name Date 533,837 Bott Feb. 5, 1895710,124 Tasker Sept. 30, 1902 718,719 Meigs et al. Jan. 20, 19031,434,044 Cooke Oct. 31, 1922 2,165,263 Holm July 11, 1939 2,405,414Eksergian Aug. 6,1946

2,406,537 Goehmann Aug. 27 1946 FOREIGN PATENTS Number Country Date468,583 Great Britain July 8, 1937

